Dark Impulse
by XRabbit14
Summary: Dusttale fanfiction. In the works, will be updated infrequently. Sans is slowly falling into madness and must figure out how to deal with himself throughout the copious resets, and the trauma inflicted on him by the human transversing the Underground. Language and violence, and some gore advisory. Please proceed with caution.
1. Chapter 1

_**"Brother, don't-!"**_

Sans immediately dropped the knife, looking down to his visibly shaking hands.

Why was he shaking? Why couldn't he stop? How did he get that knife? What was he doing with it?

And most importantly… why was he approaching his brother with it?

The loud clattering sound that was heard as the metal hit the cold tile floor echoed in Sans' ears, but it didn't deter him from his shocked state.

Papyrus stood there, lowering his hands from a defensive position, and breathed a sigh of relief as he looked over his wide-eyed brother. He knew something was off with him, but that was to be addressed at a different time. For right now, it was clear that he needed The Great Papyrus' support.

Kneeling down quietly, Papyrus slowly picked up the semi-large knife, and carefully rose back up again to place it on a nearby counter - out of sight, and out of the way.

Sans brought his hands to his face, letting the small bones of his fingers rest just inside the sockets of his eyes - his eyes devoid of any pupils, and it was just the solid blackness of the lack of them that consumed him.

"Brother… it's going to be alright. Whatever is bothering you, you can tell me."

Papyrus assured, as he turned from the counter and to Sans again, opening his arms and kneeling down to hug his smaller skeleton sibling.

Sans said nothing, he just merely stood there, trembling within Papyrus' embrace.

 _Why?_

Why this?

He didn't know what had come over him, he had become so desperate for something in that moment, but he didn't even know for what.

His brother's embrace was comforting, but it wasn't enough to snap him out of the dark abyss his mind had plunged into.

He slowly removed his hands from his eye sockets, and slowly began to hug Papyrus back, gripping onto the vast amount of red fabric that was his tattered, battle-worn scarf.

He closed his eyes.

It was soft. He could at least feel that.

It, almost felt like…

He sat up in bed.

 _Bedsheets._

 _"Wh-... What the hell..?"_

He looked down, at his mess of a bed.

His various blankets were strewn everywhere - a sign of yet another sleepless night of tossing and turning.

Sighing, Sans blinked a few times, resting one hand on the sheets and bringing the other to his head.

"It was just a dream…"

He assured himself quietly, but it felt all too real to him nonetheless…

Getting up, he adjusted the clothes he had slept in, consisting of his normal everyday attire.

He had been too tired to change, again.

Quickly stepping into his sneakers, his socks nearly halfway off of his feet, he made no effort to tie the laces as he exited his dull, messy room.

"Brother? Is that you?"

"Yeah, I'm comin' Paps."

Sans stepped down the stairs, keeping his head forward to scan the living room for his sibling's all too familiar voice. There, stepping out of the kitchen, was Papyrus, engaging in his normal everyday morning routine. He smiled that big perma-grin of his as he watched him descend the rest of the stairs.

"Ah, Sans! You're just in time for breakfast! You're usually not up so early, I'm surprised!"

Reaching the last step, Sans looked up at his taller partner, with a half smile, and made eye contact; his sunken in sockets contrasting heavily with Papyrus' lively looking ones.

"Heh… just couldn't wait for breakfast this morning, I suppose."

He shrugged, letting out a small, inaudible sigh.

Papyrus raised a brow.

"Sans… are you not feeling well? You haven't made one of your awful puns yet, which is very strange for you. Usually you would have said something by now."

"Eh, just can't think of anything right now. I'll be sure to get back to you on that, bro."

He looked away, his eyes drooping into a sullen expression.

Before Papyrus could say anything in response, he noticed that Sans was staring behind him - into the kitchen.

His pupils disappeared.

 _He had seen the knives._

Papyrus' facial expression contorted into one of worry, as he didn't know what had seemingly frightened Sans, or why it had. He didn't at all like seeing him this way.

"...Hey, uh, Paps, change of plans. I'm goin' to work early today."

Sans said, turning around abruptly, pulling his gray hood up to hide his face, and disappearing all in one motion.

Papyrus choked back words, as Sans had teleported away from sight, not even taking any time to say goodbye. After a moment, he closed his jaw, turning around to look into the kitchen, his sight glossing over the knives placed into a holding block on the counter.

"...I'm worried for you, brother."

Papyrus admitted quietly to himself, before picking up right back where he left off in his morning regimen.

\--

The small-statured monster pushed open one of the heavy doors into Grillby's, some monsters absent as Sans observed.

Understandably so, as it was still somewhat early in the morning, he thought to himself.

His footsteps sounded against the floorboards, in slow, dragging footsteps, before approaching the main counter where the fire elemental running the place was standing.

"Heya Grillbz."

Sans greeted, hoisting himself up onto the small stool, taking a seat and immediately hunkering over the bar, removing his hood and letting the fabric sink to sit around his shoulders, where it usually lay.

"...You're early."

Grillby spoke softly, observing his regular customer after a long pause.

"Couldn't sleep."

Sans dismissed.

"I'll take the usual."

The bartender nodded slightly, reaching under the counter for a bottle of ketchup he had already set in place, just waiting for Sans.

He set it on the counter, his glasses gleaming slightly in the artificial light of the restaurant.

"Thanks. I really need it this morning."

Sans admitted with a tired tone, taking the bottle as Grillby pushed it towards him lightly.

Grillby spoke again.

"I can't suppose you've been having those nightmares again?"

The exhausted skeleton went quiet.

"...I had another one last night, Grillbz."

The bartender looked over Sans, noting his visible lack of energy - which was even more noticeable than usual. Setting a white dish cloth and a wine glass that he had been cleaning aside, he leaned over, setting his arms on the counter before him, listening.

"What was it about this time."

Sans' pupils shrunk into nothingness once more, removing the white glow from his eyes.

"...Paps."

Grillby's face somehow seemed to show concern upon hearing this, despite having a lack of one.

"...I won't ask for details. I know how much your brother means to you - but I'm sorry to hear that, Sans."

Grillby replied calmly, but solemnly.

The whole restaurant seemed to be eerily silent. In fact, it had been ever since Sans had walked in, despite there being people in it. Sans seemed to guess that they weren't very talkative in the morning, he supposed. It was as if the whole establishment knew, even though their conversation hadn't been loud at all. In fact, Grillby was usually a very soft-spoken individual, yet Sans could hear him clear as day, as there weren't any sidebar conversations taking place at the time to distract him from concentrating on listening to the bartender in front of him.

Sans lifted the bottle filled with the red condiment to his teeth, saying; "Yeah, I am too." before he took a drink, his pupils returning back shortly after doing so.

Grillby watched him intently, a question burning in his mind.

"...Do you think your nightmares have anything to do with the disappearances as of late? ...I don't blame you if they have had an impact on you, too. Everyone in Snowdin is terrified."

Sans nearly choked on his drink. He coughed a few times, bringing a balled fist up to his mouth as he did so.

"I'm sorry, I didn't mean to be so bold with my statement. I was just curious-"

 _"What disappearances??"_ Sans cut him off as soon as he had gotten done with his coughing fit, leaning in more towards Grillby, now suddenly desperate for answers.

Grillby looked at him in confusion.

"...I thought you would've been one of the first to notice, Sans. I'm surprised at you."

 _"Grillbz."_

Sans prodded, demanding answers.

Grillby sighed, a fair bit amount of hazy smoke exiting his mouth upon doing so. He picked up his cleaning cloth and began to wipe down another dish, this being a whiskey glass.

"...Look around my establishment, Sans. It's not hard to see that some of my regulars are gone."

"...well, yeah, but…"

Sans brought a hand up to his mouth in thought, staring intently down at the wood-top counter, studying the patterns of the wood.

Grillby waited for an answer, but didn't get one in response as Sans couldn't speak up to protest.

 _"...It's gotta be the human. It has to be…"_

The hollow skeleton concluded to himself, clenching his other hand resting on the counter slowly to form a fist subconsciously.

Sans rose from his seat, leaving the hardly-touched ketchup bottle.

He tossed a few spare gold pieces onto the counter, much to Grillby's surprise, as Sans never paid his tab.

"Thanks for the drink, bud. I'll be sure to come back later to get some more," Sans paused, looking towards the door as he pulled his hood back up, stopping after a few steps forward to finish his sentence as he looked to the side.

 _"...I'll sure as hell be needing it."_

\--

The hooded skeleton paced through the snow, his laces dragging behind him as he did so.

 _"Why would the human be taking out more… lesser known monsters first, while trying to make an effort not to be seen? It just doesn't make any sense… Surely someone would have seen them by now and the whole town would have known soon enough."_

Sans pondered, shadows covering his face as he looked down while crossing the long, rickety wooden bridge that connected two steep, jagged cliffs.

 _"...And wouldn't Toriel have told me about someone coming through the Ruins by now?"_

He stopped directly in the middle of the bridge, suddenly getting the urge to look over the side of the wooden panels beneath his feet, which he did so.

He nearly lost his balance.

 _ **Bodies.**_

God, they were everywhere… everyone he knew, saw, and had come to grow accustomed to had been mercilessly thrown over the bridge to their deaths… Their limbs mangled, twisting in unnatural positions, entwining with each other's.

He took a step back, catching himself on the parallel rope just behind him, his heart nearly jumping through his ribcage at the sudden scare at him falling backwards and ending up like the rest of them.

He clenched his eyes shut, not believing what he saw.

He had seen many things over the course of all the different resets, but this… this was something entirely different and new to him.

The thought that the human could somehow do this, or wanted to, didn't even occur to him.

Taking a shaky and hesitant breath, he reopened his eyes, daring to take another peek over the bridge and to the sharp rocks below.

...They were gone.

All of the horrific mangled corpses of his friends were gone.

He choked out, as if to protest, but couldn't find the strength to say anything. Only to scream internally. So many thoughts were racing through his mind, he couldn't comprehend all of them at once.

Not being able to take his sight off of the stones below, and how he had seen in detail how limbs were almost embracing the sharp edges of the rocks themselves, any body part that could be ripped into was- he almost lost his grip and nearly fainted.

Instead, with what little strength he had remaining of the encounter, he quickly teleported just a few feet away to the other end of the bridge, collapsing to his knees.

Sinking into the snow, he felt the sensation of tears welling into his deep-set eye sockets, his small white pupils shaking back and forth rapidly in fear.

The realization hit him that he was losing it.

What little sanity he still had ahold of was slowly slipping away from him, and there was nothing he could do about it.

After so many times, so many runs, so many endings that he had seen and had been just as easily taken away from him - after he had been through all of the emotions and feelings on the spectrum, he was finally beginning to lose his sense of sanity and his sense of self.

And that, was _**horrifying.**_

He had cursed the same damned human millions of times, both verbally and mentally for this. _**They**_ were the source of the problem. That two-faced backstabbing son of a bitch was gonna get it.

 _...One of these times._

One of these times, Sans was finally going to kill them, and they would stop coming back to ruin his life and torment him for as long as they already had been.

 _...Right?_

\--

 **Author's Note:**

 _Hey gang! I hope you all enjoyed the first chapter of the story. Now I will admit, I didn't know much about Dusttale to begin with, but I thought it was a really neat idea and it inspired me to make my own rendition of it. So if I don't get some things right, just keep that in mind. The credit for the idea goes to it's proper owners, I just own the story. Anyways, I hope y'all stick around for the next chapter! I'll be sure to work on it as soon as possible._

 _Also, if you can guys, be sure to leave a review so I can improve and to boost my motivation and confidence. Thanks!_ _**-M**_

 **P.S.**

 _I seem to be having trouble editing my story. I'm doing it on the app, so I'm not sure if that's the problem, but If you've read the chapter you may have gotten confused as to where the time skips are, or where the story takes place in a different setting. No matter what I try, it doesn't work when I try to separate those parts. I've tried dashes, spaces, periods, you name it. So if someone could help me out and leave a comment or something I will be forever grateful and I'll be sure to fix that asap. Thank you!_ _ **-M**_

 **Update:**

 _Thank you so much to Wingah for helping me solve my previous issue! Thanks to your kind review, the different scenes in the story are now separated, and much easier to make out. Thanks again!_ _**-M**_


	2. Chapter 2

After spending close to about 30 minutes trying to recover from his hallucination scare, and holding back tears, Sans was now running through the forest, and his hood had flown back from the sheer velocity from his efforts to try and distance himself as far away from that damned bridge as possible.

It was scary to think that he had almost died there.

It was scary to think that _anyone_ could have died there, and their dust could just as easily be floating around the bottom of the cliffs, dancing along the edges of the rocks and clinging to the gently drifting snowflakes.

His panting could be heard from nearly a mile away as he neared the Ruins door, desperate to talk to the old lady that had broken away from her own kingdom.

 _"Man, I really am gettin' out of shape…"_

Sans scolded himself mentally, while finally coming to a stop at the door, snow swirling around him as he hunched over to catch his breath.

He closed his eyes for a moment, feeling his ribcage expand and deflate with each deep breath he took. His eyes reopened, just slightly, once more to take a look at the tall, ornate purple door, with matching cracked and aged stone surrounding the doorway.

He kept his gaze down, and that's when he noticed something was off.

The heavy, large door, was slightly ajar.

"...Tori…?"

Sans called out to her in a questioning voice, very obviously confused as usually, the old woman was hellbent on keeping that thing shut at all costs.

 _...Until the human wanted to pass through._

He quickly straightened himself out, taking a few measly steps forward, observing the crack in the door.

He couldn't tell by the snow, as a new layer had already blanketed and covered up whoever had been there previously, but it seemed as if someone from the other side had opened the door, stepped out, then tried to close it again, but couldn't get it shut all the way. Or, maybe they didn't have the manners or care to close it fully. Who knew.

Sans didn't hesitate to wrap his boney fingers along the edge of the door and pull towards him to open it once more.

He had to find Toriel.

...Or, what was left of her, if the human really had gone through here.

With a grunt, and the sound of light snow being rustled, he successfully pulled the door open enough to slip through and walk inside the exit to the Ruins.

"Tori?"

He called out for her again, this time in a slightly louder volume.

The sound of his question echoed off of the mauve brick, and bounced back at him, almost as if to mock him of the lack of answer.

A shaky sigh left his teeth, and he shoved his hands into the pockets of his hoodie, hesitantly making his way down the long, dark corridor.

He didn't like this.

He didn't like this at all.

Only on very few runs did he have to intrude like this, but he hated it every time.

But… this time, something felt… off.

 _Very_ off.

Like he wasn't welcome here.

He didn't know if it was because of the human, wanting to take an exceedingly malice route this time, just to mess with him, or for their own pleasure; or if it was him and his ever slipping sanity that he was oddly aware of.

Maybe it was some kind of mixture of the above options, or something different entirely.

After turning a few corners, he eventually reached the steps, which he began to ascend.

The stairs squeaked uncomfortably beneath his feet, making a lot of sound to disrupt the disturbingly quiet aura that seemed to envelope the place.

Upon setting foot on the first landing, he stopped, looking around the small landing room through the wooden rungs of the sturdy guard rails, only for his eyes to meet nothing out of place.

He furrowed his brow bone, venturing up the last few steps before fully coming to the entrance of the usually cozy home.

...It was, freezing.

And this was unusual, as the goat lady always had made an effort to make her small abode as lively and warm as possible to invite any unlikely newcomers or passer-bys that may have fallen down the hole to the Underground.

Instead, he couldn't feel the difference between this place and the outside of Snowdin.

Even the lights were somehow dimmer, getting rid of any warm light that may have once resided and cast a glow that bounced off of the walls and settled onto the floor.

He called out to her again, and yet again, got no response in return.

Looking to his left, he gazed down the long hallway, to where the bedrooms lie.

He shrugged, deciding not to overstay his welcome, as he was already technically trespassing anyways.

The last thing he wanted to do was snoop around someone's other things.

 _ **Besides, this place was giving him the creeps.**_

Glancing the other way into the living room, he didn't see Toriel in her usual reading chair next to the fireplace, or at the large dining table, either.

From all he could tell, things were… fine, if he dare say that.

It felt very wrong to say that.

"Maybe she's just… out, doing stuff. Yeah. Gotta be."

Sans tried to assure himself, but it didn't do anything to calm the ever rising sense of dread that was slowly consuming him.

Walking across the tightly packed floorboards, he made his way to the front door, opening it, only to be greeted with a bright, blinding, yellow light.

The small skeleton winced, and stumbled back a bit as he was caught off guard, his hand never leaving the door knob.

After a few moments, the light faded, and revealed something terrible.

 _"...Was it always this dusty..?"_

Sans opened the door fully, and in the soft yellow light that was coming from the very right of him, it illuminated billions of dust particles, floating around, covering the stray rose-colored leaves at his feet.

It was as if the motion of the door swinging open had kicked up the silver dust, only to greet the monster with yet another terrifying sight.

His glowing white pupils were the size of pinpricks as his breathing got unsteady, and he surveyed the area, his gaze finally shifting to the right where the soft golden haze was coming from.

His vision quickly adjusted to the unearthly, yet inviting glow of a bright star.

 _Was this always here? Why hadn't he noticed it before? No… why couldn't he see it before?_

Placing one foot in front of the other, he carefully approached the light as it danced in the same spot before him, hovering just above the ground.

 _Was he imagining things?_

Without thinking, he reached out to grasp it.

...Nothing.

The bones of his fingers went through it like it was nothing, and he didn't feel anything upon touching it either.

And here he was, fully expecting for it to burn him somehow, or at least transport him to a magical dimension or something.

He scoffed, drawing his hand back, thinking that this was all some sort of hallucination, like the one he had experienced from earlier.

He looked back to the gnarled, dark tree that innocently stood in the middle of the path leading up to the queen's small shack, feeling his nerves calm a little as he settled on the thought that all of this wasn't actually real.

 _ *** ERROR: Not enough DETERMINATION to use save point.**_

He had only blinked for a second, and an error message had seemingly appeared to him telepathically.

The words were somehow burned into his mind.

He snapped his head back over to where the save star had been, only to see that it - along with the light that it had cast over the small cave-like area - had disappeared.

He couldn't see the dust anymore; perhaps it was too dark, or perhaps it had settled.

Either way, he wasn't sticking around to find out if it was real or not, as the brick walls were starting to close in on him in the dim, dusky light.

\--

That night, the troubled skeleton lay awake in his bed, unable to sleep as he laid on his side and stared at the wall next to him, the moonlight pouring in through the window above where his skull rest on a pillow.

The sheets were thrown haphazardly over him, yet he had no motivation to fix them, even though he was cold - his mind was somewhere else entirely.

The dreams.

The disappearances.

The hallucinations.

The bodies.

The dust.

That weird light…

None of it made any sense, but his mind just kept going over and over the same few things, in a mad cycle to even try and begin to grasp what the hell was going on.

The only solution - if you could even call it that - that he could come up with was that it was all linked to the human somehow.

Even his sanity.

Of course they had finally gotten to him, but, this didn't explain anything else - at least that's what he believed.

It certainly didn't explain what he saw, either.

That phrase just kept echoing in his mind, almost as if it were calling to him from somewhere beyond his comprehension.

 _"Not enough DETERMINATION."_

He shifted, and turned - laying on his other side to stare at the opposite wall to his room.

"Not enough determination, huh…?"

He repeated to himself, speaking softly in the dark room.

He closed his eyes.

Something was urging him to get more, but he knew what he'd have to do in order to get it, and he did _**not**_ want to have to go to those extremes unless it was absolutely necessary.

\--

Toriel ran.

She ran as fast as she possibly could, ripping her dress from stretching the seams too far in her efforts.

She looked back, a horrified expression painted across her features as she screamed, almost slipping up the stairs out of fear.

Using her fire magic, she made tall, orange flames rise up out of the ground, stopping her pursuer in their tracks. It kept them at bay while she stumbled up the stairs to the interior of her home, giving her time to try and find a place to hide.

The pads of her large paws sounded with thundering footfalls up the stairs and down the small hallway to her room, turning corners sharply, nearly dragging the banisters with her as she passed them.

She clawed for the doorknob, heart nearly jumping out of her chest as she fumbled with it for a few seconds. Finally getting a grip on it and turning it roughly, she swung the door open inwards and slammed it behind her after throwing herself into the small room. Desperately, she panicked and grabbed the nearest thing - this being her desk chair - and propped it up under the doorknob to effectively keep her hunter from opening it from the other side.

Backing up slowly, she collapsed onto the floor, her back sliding roughly down the bookcase that faced the entrance to the room.

Quiet sobs left her throat as soon as they started to creep their way up and take over her. She brought her large hands to her face, hot tears spilling onto them and trailing down her cheeks, soaking into her white fur that stood on end from being so scared.

She brought her knees up to her chest, propping her elbows up so she could be as tiny as she possibly could.

This went on for awhile, her trembling figure crying on the floor, her hands gripping at the fur on her head over her eyes to try to shelter herself from the horror that was just beyond her bedroom door.

A strong hand suddenly firmly grasped one of her wrists, yanking it away from her face, as she squealed and looked up in terror.

 _ **"Shut up."**_

She could only let out one last, shrill sound of agony before it turned into a disgusting gurgling noise, as the sharp edge of the blade was pointed to her neck and gouged into it, cutting deeply into her esophagus and trachea. Blood gushed from the wound as her eyes glazed over, her eyesight becoming blurry as major arteries were cut and any chance of her breathing properly again was diminished into nothing.

As the knife was pulled away, she felt pain, but she also felt the hand that was being held let go, and it dropped to the floor. Her other one that was still covering her eye slowly slid down the side of her face. She managed to weakly grasp at her wound, trying to stop the bleeding to the best of her ability, but to no avail.

Her ears ringing, and her vision going from blurry to black, she felt her life fading away slowly as the lack of oxygen and loss of blood worked together in harmony to kill her, and the very last sound she heard was the knife being dropped, followed by slow footsteps that faded into nothingness.

Sans bolted upright in bed, a cold sweat forming on his face and all over his body.

He wanted to scream, but his throat locked up aside from his heavy breathing, and he couldn't make any sound.

He gripped his blanket close to his chest, as after just a moment, he had started to hyperventilate from the horrid severity of his nightmare.

 _ **"What the fuck was that?!?"**_

His mind screamed at him as tears freely poured from his eye sockets, and disappeared into bluish particles as gravity inevitably pulled them down to his chin and fell onto the fabric below.

He cried helplessly as he tried to calm himself down, but not before letting his fear consume him for a time. But soon enough, his breathing finally slowed, and the tears eventually stopped.

Pulling his arm up to his face, he used the sleeve of his familiar navy blue hoodie to dry the tear tracks that had been left behind.

 _Silence._

Not even the branches of the pine trees outside his room window seemed to rustle with any sort of breeze.

That's when he looked up, at the blank walls in front of him with an agonized look in his eyes - and concluded to himself.

 _"...I need to find Tori."_

 _\--_

 **Author's Note:**

 _Hey guys! Thanks for tuning in to the second chapter! I am so grateful for all the positive feedback I've been getting so far, and that was only on chapter one! I hope this chapter is just as well-received. I'm really happy with where this is going so far! I've never been so excited to type a story before :)_

 _On another note, I did want to address something else. It appears that I can only leave two or so responses to reviews per chapter, so that's pretty lame. I wanted to stay in touch with you guys, but it appears that the first two people will get responded to and everyone else will not unfortunately. It really sucks, but I guess it's gonna be a first come, first serve basis. I know not many people really care about this, but I just thought I'd address it nonetheless._

 _Though that does not mean I won't address any questions or reviews after the first two people have already submitted their comments! I'll just have to respond to anything else I get asked or told in the Author's Note of the next chapter I release. And if I get a bunch of questions, or multiple of the same (which I highly doubt will happen), I'll just compile a QA! So don't be afraid to ask something if you're confused. I won't answer everything - as I do want to keep at least some element of mystery and suspense to the story - but I'm pretty open, so I'll address any questions or concerns y'all might have._

 _Anyways! I hope y'all enjoy! Sorry for the long Author's Note lol. But don't forget to leave a review on what you liked or what I could improve on! It really helps! Thank you guys so much!_ _I'll see y'all in the third chapter ;)_ _ **-M**_


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